# Copyright (c) 2007-2008 Pedro Matiello <pmatiello@gmail.com>
#                         Salim Fadhley <sal@stodge.org>
#
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# obtaining a copy of this software and associated documentation
# files (the "Software"), to deal in the Software without
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"""
Set of heuristics to be used with A*.
"""


# Imports
import warnings


# Edmond Chow's heuristic

class chow(object):
	"""
	An implementation of the graph searching heuristic proposed by Edmond Chow.

	For details, check: http://www.edmondchow.com/pubs/levdiff-aaai.pdf 
	"""
	
	def __init__(self, *centers ):
		"""
		Initialize a Chow heuristic object.
		"""
		self.centers = centers
		self.nodes = {}
		
	def optimize( self, thegraph ):
		"""
		Build a dictionary mapping any node to a chow sequence for that node.
		"""		
		for center in self.centers:
			shortest_routes = thegraph.shortest_path( center )[1]
			for node, weight in shortest_routes.items():
				self.nodes.setdefault( node, [] ).append( weight )
		
	def __call__( self, start, end ):
		"""
		Estimate how far start is from end.
		"""
		assert len( self.nodes.keys() ) > 0, "You need to optimize this heuristic for your graph before it can be used to estimate."
				
		cmp_sequence = zip( self.nodes[start], self.nodes[end] )
		chow_number = max( abs( a-b ) for a,b in cmp_sequence )
		return chow_number